Changeset 17076 for trunk/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Hashing/SymbolicExpressionTreeHash.cs

Timestamp:

07/05/19 10:26:41 (5 years ago)

Author:

gkronber

Message:

#2950: made some small changes while reviewing.

File:

• trunk/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Hashing/SymbolicExpressionTreeHash.cs (modified) (4 diffs)

trunk/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Hashing/SymbolicExpressionTreeHash.cs

@@ -48 +48 @@
       ulong hashFunction(byte[] input) => HashUtil.DJBHash(input);
 
-      var hashNodes = simplify ? node.MakeNodes(strict).Simplify(hashFunction) : node.MakeNodes(strict).Sort(hashFunction);
+      var hashNodes = simplify ? node.MakeNodes(strict).Simplify(hashFunction) : node.MakeNodes(strict).Sort(hashFunction); // simplify sorts implicitly
       var hashes = new ulong[hashNodes.Length];
       for (int i = 0; i < hashes.Length; ++i) {
@@ -210 +210 @@
       var treeNodes = nodes.Select(x => x.Data.Symbol.CreateTreeNode()).ToArray();
 
+      // construct tree top down (assumes postfix order for nodes)
       for (int i = nodes.Length - 1; i >= 0; --i) {
         var node = nodes[i];
@@ -244 +245 @@
     // (in other words simplification should be applied in a bottom-up fashion)
     public static ISymbolicExpressionTree Simplify(ISymbolicExpressionTree tree) {
-      ulong hashFunction(byte[] bytes) => HashUtil.JSHash(bytes);
-      var root = tree.Root.GetSubtree(0).GetSubtree(0);
+      ulong hashFunction(byte[] bytes) => HashUtil.DJBHash(bytes);
+      var root = tree.ActualRoot();
       var nodes = root.MakeNodes();
       var simplified = nodes.Simplify(hashFunction);
@@ -369 +370 @@
         nodes[i].Enabled = false;
       } else if ((parentSymbol is Exponential && childSymbol is Logarithm) || (parentSymbol is Logarithm && childSymbol is Exponential)) {
+        // exp(log(x)) == x only for positive x. We consider this as equivalent for hashing anyway.
         child.Enabled = parent.Enabled = false;
       }